Vein occlusion assessment using temperature

ABSTRACT

A medical system, comprising an ablation catheter is disclosed. The ablation catheter includes an elongate shaft with a proximal end, a distal end and a lumen disposed between the proximal end and the distal end. The ablation catheter also includes an expandable element in fluid communication with the lumen, a first temperature sensor operable to measure a first temperature; and a second temperature sensor operable to measure a second temperature. The first temperature sensor and the second temperature sensor are longitudinally separated from each other by at least a portion of the expandable element.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional of patent application Ser. No.13/799,714, filed Mar. 13, 2013, entitled VEIN OCCLUSION ASSESSMENTUSING TEMPERATURE, the entirety of which is incorporated herein byreference.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

n/a

FIELD OF THE INVENTION

The present invention relates to relates to catheter-based methods,systems and devices for occlusion, and in particular, utilizingmeasurements of one or more physiological parameters to guide anablation treatment of cardiac arrhythmias.

BACKGROUND OF THE INVENTION

Catheter based devices are employed in various medical and surgicalapplications because they are relatively non-invasive and allow forprecise treatment of localized tissues that are otherwise inaccessible.Catheters may be easily inserted and navigated through the blood vesselsand arteries, allowing non-invasive access to areas of the body withrelatively little trauma. Recently, catheter-based systems have beendeveloped for implementation in tissue ablation for treatment of cardiacarrhythmias such as atrial fibrillation, supra ventricular tachycardia,atrial tachycardia, ventricular tachycardia, ventricular fibrillation,and the like. One such implementation involves the use of fluids withlow operating temperatures, or cryogens, to selectively freeze, or“cold-treat”, targeted tissues within the body.

The cryogenic treatment involves cooling a portion of the catheter to avery low temperature through the use of the cryogenic fluid flowingthrough the catheter. A cryogenic device uses the energy transferderived from thermodynamic changes occurring in the flow of a cryogentherethrough to create a net transfer of heat flow from the targettissue to the device, through conductive and convective heat transferbetween the cryogen and target tissue.

Structurally, cooling can be achieved through injection of high-pressurecoolant into a lumen of the catheter. Upon injection, the refrigerantundergoes two primary thermodynamic changes: (i) expanding to lowpressure and temperature through positive Joule-Thomson throttling, and(ii) undergoing a phase change from liquid to vapor, thereby absorbingheat of vaporization. The resultant flow of low temperature refrigerantthrough the device acts to absorb heat from the target tissue andthereby cool the tissue to the desired temperature.

Once refrigerant is injected into the lumen, it may be expanded insideof an expandable element (chamber), which may be positioned proximal tothe target tissue. In embodiments, the expandable element may also bethermally conductive. Devices with an expandable element, such as aballoon, may be employed. In such devices, refrigerant is suppliedthrough a catheter lumen into an expandable balloon coupled to suchcatheter, wherein the refrigerant acts to both: (i) expand the balloonnear the target tissue for the purpose of positioning the balloon, and(ii) cool the target tissue proximal to the balloon to cold-treatadjacent tissue.

The expandable element may also serve a second function; blocking theflow of blood through the desired treatment site (occlusion). Thecatheter is typically of a relatively small diameter and long body,generally determined, by the diameter and length of the vascularpathways leading to the ablation site. The coolant in the catheter ishighly susceptible to conductive warming effects due to the relativeproximity of the catheter (and coolant) to the body tissue and blood.Furthermore, the rate of cooling is limited by the ability to circulatea sufficient mass flow of coolant through the catheter. Yet there is arequirement that the coolant itself be at a sufficiently lowtemperature, in some cases below freezing, at the location of theablation. In addition, while this may be generally true, the occlusionmay help reduce the heat-load at the target ablation site and not on thewhole catheter.

Blocking the flow of blood using the expandable element allows moreeffective cooling which facilitates the treatment process and may reducethe treatment period. Effective contact to achieve occlusion may requiremoving, positioning, anchoring and other mechanisms for locating andstabilizing the conformation of the expandable element of the catheter.Moreover, slight changes in orientation may greatly alter thecharacteristics of the catheter, so that even when the changes arepredictable or measurable, it may become necessary to providepositioning mechanisms of high stability or accuracy to assure adequatetreatment at the designated sites. Furthermore, one must assure that theablation is effective at the target tissue.

Known techniques for visualizing the contact between the expandableelement and the target tissue include the use of radiographically opaquecontrast medium to enable radiographic-mapping of the target tissueduring application and operation of the catheter. Such an imagingtechnique may not be desirable due to the use of contrast medium and itsinteraction with the patient tissue. Additionally, it may be desirableto eliminate or minimize the exposure of both patient and clinician tothe radiographic-mapping waves used for imaging.

It is desirable therefore, to provide improved catheter systems that arecapable of providing an indication of occlusion while eliminating orsignificantly reducing exposure of the patient and clinician to imagingwaves.

SUMMARY OF THE INVENTION

The present invention advantageously provides a method and system fordetermining occlusion in a blood vessel. In accordance with oneembodiment, a medical system comprising an ablation catheter isdisclosed. The ablation catheter includes an elongate shaft with aproximal end, a distal end and a lumen disposed between the proximal endand the distal end. The ablation catheter also includes an expandableelement in fluid communication with the lumen, a first temperaturesensor operable to measure a first temperature, and a second temperaturesensor operable to measure a second temperature. The first temperaturesensor and the second temperature sensor are longitudinally separatedfrom each other by at least a portion of the expandable element.

In accordance with another embodiment, a method of assessing veinocclusion with an ablation catheter is disclosed. The ablation catheterincludes an elongate shaft with a proximal end, a distal end and a lumendisposed between the proximal end and the distal end. The ablationcatheter also includes an expandable element in fluid communication withthe lumen. The method includes measuring a first temperature using afirst temperature sensor, and measuring a second temperature using asecond temperature sensor. The first temperature sensor and the secondtemperature sensor are longitudinally separated from each other by atleast a portion of the expandable element.

In accordance with yet another embodiment, a medical system isdisclosed. The medical system includes an ablation catheter and acontrol unit. The ablation catheter includes an elongate shaft with aproximal end, a distal end, a lumen disposed between the proximal endand the distal end, and an expandable element in fluid communicationwith the lumen. The ablation catheter also includes a first temperaturesensor operable to measure a first temperature, and a second temperaturesensor operable to measure a second temperature. The first temperaturesensor and the second temperature sensor are longitudinally separatedfrom each other by at least a portion of the expandable element. Thecontrol unit is operable to deliver a continuous flow of inflation fluidto the expandable element, and determine an extent of occlusion in ablood vessel when the expandable element is inserted within the bloodvessel and inflated. The determination is being based at least in parton a temperature differential between the first temperature and thesecond temperature.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete understanding of the present invention, and theattendant advantages and features thereof, will be more readilyunderstood by reference to the following detailed description whenconsidered in conjunction with the accompanying drawings wherein:

FIG. 1 is an illustration of an example of a medical system constructedin accordance with the principles of the present invention;

FIG. 2 is an illustration of an example of a medical device assemblyconstructed in accordance with the principles of the present invention;

FIG. 3 is another illustration of an example of a medical deviceachieving full occlusion constructed in accordance with the principlesof the present invention; and

FIG. 4 is still another illustration of an example of a medical deviceachieving partial occlusion constructed in accordance with theprinciples of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to the drawing figures in which like referencedesignations refer to like elements, an embodiment of a medical systemconstructed in accordance with principles of the present invention isshown in FIG. 1 and generally designated as “10.” The system 10generally includes a medical device 12 that may be coupled to a controlunit 14 or operating console. The medical device 12 may generallyinclude one or more diagnostic or treatment regions for energetic,therapeutic and/or investigatory interaction between the medical device12 and a treatment site or region. The diagnostic or treatment region(s)may deliver, for example, cryogenic therapy, radiofrequency energy, orother energetic transfer with a tissue area in proximity to thetreatment region(s), including cardiac tissue.

The medical device 12 may include an elongate body 16 passable through apatient's vasculature and/or proximate to a tissue region for diagnosisor treatment, such as a catheter, sheath, or intravascular introducer.The elongate body 16 may define a proximal portion 18 and a distalportion 20, and may further include one or more lumens disposed withinthe elongate body 16 thereby providing mechanical, electrical, and/orfluid communication between the proximal portion of the elongate body 16and the distal portion of the elongate body 16, as discussed in moredetail below.

The medical device 12 may include an elongate shaft 22 at leastpartially disposed within a portion of the elongate body 16. Theelongate shaft 22 may extend or otherwise protrude from a distal end ofthe elongate body 16, and may be movable with respect to the elongatebody 16 in longitudinal and rotational directions. That is, the elongateshaft 22 may be slidably and/or rotatably moveable with respect to theelongate body 16. The elongate shaft 22 may further define a lumen 24therein for the introduction and passage of a guide wire. The elongateshaft 22 has a proximal end, a distal end and a lumen 24 disposedbetween the proximal end and the distal end. The elongate shaft 22 mayinclude or otherwise be coupled to a distal tip 26 that defines anopening and passage there through for the guide wire.

The medical device 12 may further include a fluid delivery conduit 28traversing at least a portion of the elongate body and towards thedistal portion. The delivery conduit 28 may be coupled to or otherwiseextend from the distal portion of the elongate body 16, and may furtherbe coupled to the elongate shaft 22 and/or distal tip of the medicaldevice 12. The fluid delivery conduit 28 may define a lumen therein forthe passage or delivery of a fluid from the proximal portion of theelongate body 16 and/or the control unit 14 to the distal portion and/ortreatment region of the medical device 12. The fluid delivery conduit 28may further include one or more apertures or openings therein, toprovide for the dispersion or directed ejection of fluid from the lumento an environment exterior to the fluid delivery conduit 28.

The medical device 12 may further include one or more expandableelements 30 at the distal portion of the elongate body 16. Theexpandable element 30 may be coupled to a portion of the elongate body16 and also coupled to a portion of the elongate shaft 22 and/or distaltip 26 to contain a portion of the fluid delivery conduit 28 therein.The expandable element 30 defines an interior chamber or region thatcontains coolant or fluid dispersed from the fluid delivery conduit 28,and may be in fluid communication with an exhaust lumen 32 defined by orincluded in the elongate body 16 for the removal of dispersed coolantfrom the interior of the expandable element 30. The expandable element30 may further include one or more material layers providing forpuncture resistance, radiopacity, or the like.

A first temperature sensor 62 is coupled to medical device 12 at alocation that may be anterior or distal to the expandable element 30. Asecond temperature sensor 64 may be coupled to medical device 12 at alocation that may be posterior or proximal to the expandable element 30,i.e., the first temperature sensor 62 is positioned distal to theexpandable element, and the second temperature sensor is positionedproximal to the expandable element. The first temperature sensor 62 andthe second temperature sensor 64 may be longitudinally separated fromeach other by at least a portion of expandable element 30. The firsttemperature sensor 62 and the second temperature sensor 64 may belocated anywhere on the medical device 12.

The medical device 12 may further include one or moreelectrically-conductive segments or electrodes 34 positioned on or aboutthe elongate body for conveying an electrical signal, current, orvoltage to a designated tissue region and/or for measuring, recording,or otherwise assessing one or more electrical properties orcharacteristics of surrounding tissue. The electrodes 34 may beconfigured in a myriad of different geometric configurations orcontrollably deployable shapes, and may also vary in number to suit aparticular application, targeted tissue structure or physiologicalfeature. For example, as shown in FIG. 1, the electrodes 34 may includea first pair proximate to the expandable element and a second electrodepair distal to the expandable element. The electrodes 34 may bepositioned on the medical device 12 substantially equidistant from anadjacent electrode 34 in the array or may be variable distances fromeach adjacent electrode 34.

Each electrode 34 may be electrically coupled to an output portion of aradiofrequency signal generator, and each electrode 34 may also includea sensor, such as a thermocouple, an electrical conductivity sensor, aspectrometer, a pressure sensor, a fluid flow sensor, a pH sensor,and/or a thermal sensor (not shown) coupled to or in communication withthe electrodes. The sensors may also be in communication with a feedbackportion of the control unit 14 to trigger or actuate changes inoperation when predetermined sequences, properties, or measurements areattained or exceeded.

Referring again to FIG. 1, the medical device 12 may include a handle 40coupled to the proximal portion of the elongate body 16. The handle 40can include circuitry for identification and/or use in controlling ofthe medical device 12 or another component of the system. Additionally,the handle 40 may be provided with a fitting 42 for receiving a guidewire that may be passed into the guide wire lumen 24. The handle 40 mayalso include connectors 44 that are mateable to the control unit 14 toestablish communication between the medical device 12 and one or morecomponents or portions of the control unit 14.

The handle 40 may also include one or more actuation or control featuresthat allow a user to control, deflect, steer, or otherwise manipulate adistal portion of the medical device 12 from the proximal portion of themedical device 12. For example, the handle 40 may include one or morecomponents such as a lever or knob 46 for manipulating the elongate body16 and/or additional components of the medical device 12. For example, apull wire 48 with a proximal end and a distal end may have its distalend anchored to the elongate body 16 at or near the distal portion 20.The proximal end of the pull wire 48 may be anchored to an element suchas a cam in communication with and responsive to the lever 46. Themedical device 12 may include an actuator element 50 that is movablycoupled to the proximal portion of the elongate body 16 and/or thehandle 40 for the manipulation and movement of a portion of the medicaldevice 12, such as the shaft 22, and/or one or more portions of theelectrode assemblies described above, for example.

The system 10 may include one or more treatment sources coupled to themedical device for use in an operative procedure, such as tissueablation, for example. The control unit 14 may include a fluid supply 52including a coolant, cryogenic refrigerant, or the like, an exhaust orscavenging system (not shown) for recovering or venting expended fluidfor re-use or disposal, as well as various control mechanisms. Inaddition to providing an exhaust function for the fluid or coolantsupply 52, the control unit 14 may also include pumps, valves,controllers or the like to recover and/or re-circulate fluid deliveredto the handle 40, the elongate body 16, and/or the fluid pathways of themedical device 12. A vacuum pump 54 in the control unit 14 may create alow-pressure environment in one or more conduits within the medicaldevice 12 so that fluid is drawn into the conduit(s)/lumen(s) of theelongate body 16, away from the distal portion 20 and towards theproximal portion 18 of the elongate body 16. One or more valves may beincluded, for example, one may be a low pressure proportional valve andone may be a high pressure proportional valve. Both valves may becontrolled by a PID controller.

The control 14 unit may include a radiofrequency generator or powersource 56 as a treatment or diagnostic mechanism in communication withthe electrodes 34 of the medical device 12. The radiofrequency generator56 may have a plurality of output channels, with each channel coupled toan individual electrode 34. The radiofrequency generator 56 may beoperable in one or more modes of operation, including for example: (i)bipolar energy delivery between at least two electrodes on the medicaldevice within a patient's body, (ii) monopolar or unipolar energydelivery to one or more of the electrodes 34 on the medical device 12within a patient's body and through a patient return or ground electrode(not shown) spaced apart from the electrodes 34 of the medical device14, such as on a patient's skin for example, and (iii) a combination ofthe monopolar and bipolar modes.

The system 10 may further include one or more sensors to monitor theoperating parameters throughout the system, including for example,pressure, temperature, flow rates, volume, power delivery, impedance, orthe like in the control unit 14 and/or the medical device 12, inaddition to monitoring, recording or otherwise conveying measurements orconditions within the medical device 12 or the ambient environment atthe distal portion of the medical device 12. The sensor(s) may be incommunication with the control unit 14 for initiating or triggering oneor more alerts or therapeutic delivery modifications during operation ofthe medical device 12. One or more valves, controllers, or the like maybe in communication with the sensor(s) to provide for the controlleddispersion or circulation of fluid through the lumens/fluid paths of themedical device 12. Such valves, controllers, or the like may be locatedin a portion of the medical device 12 and/or in the control unit 14.

The control unit 14 may include one or more processors 37 and/orsoftware modules containing instructions or algorithms to provide forthe automated operation and performance of the features, sequences,calculations, or procedures described herein. For example, the controlunit 14 may include a signal processing unit 58 to measure one or moreelectrical characteristics between the electrodes 34 of the medicaldevice 12. Signal processing unit 58 may comprise a digital signalprocessor. An excitation current may be applied between one or more ofthe electrodes 34 on the medical device 12 and/or a patient returnelectrode, and the resulting voltage, impedance, or other electricalproperties of the target tissue region may be measured, for example, inan electrogram. Unipolar electrograms (“EGMs”) may be recorded with themapping electrode 34 as the positive electrode, and another electrode 34on the body surface or remote from the field or cardiac excitation asthe negative electrode. The control unit 14 may further include adisplay 60 to display the various recorded signals and measurement, forexample, an electrogram.

Processor 37 may be in communication, e.g., electrically coupled, tofirst temperature sensor 62 and second temperature sensor 64 to monitorthe temperatures sensed by the first temperature sensor 62 and secondtemperature sensor 64. Control unit 14 may include a receiver 33 forreceiving input signals from, for example, the first temperature sensor62 and the second temperature sensor 64, and a transmitter 35 fortransmitting signals to, for example, the first temperature sensor 62and the second temperature sensor 64. The first temperature signal fromthe first temperature sensor 62 and the second temperature signal fromthe second temperature sensor 64 may be analyzed by the signalprocessing unit 58. The processor 37 and/or the signal processing unit58 may convert signals to digital form, process those digital signals,and derive an indication of the differential temperature between thefirst temperature measured at first temperature sensor 62 and the secondtemperature measured at second temperature sensor 64. Processor 37 mayderive a temperature differential between the first temperature sensor62 and the second temperature sensor 64 based at least in part on theanalysis of the first temperature signal and the second temperaturesignal.

FIG. 2 shows an exemplary temperature sensor, such as the firsttemperature sensor 62. The first temperature sensor 62 may include aconductive element 70 that is coupled to an electrically conductive wire72 for electrical coupling of the conductive element 70 to electroniccircuitry in control unit 14, such as processor 37. The electroniccircuitry cooperates with the first temperature sensor 62 to sense thetemperature of the tissue/environment surrounding the first temperaturesensor 62. The temperature measurements may be used to provideinformation regarding occlusion. The control unit 14 may be operable todetermine a temperature difference between the first temperaturemeasured at first temperature sensor 62, and the second temperaturemeasured at second temperature sensor 64, the temperature differenceindicating the extent of occlusion in the blood vessel. The temperaturesensor of FIG. 2 may be used to implement second temperature sensor 64.

FIG. 3 includes the medical device 12, e.g., catheter 12, which operatesto treat vascular tissue of a patient that is adjacent to the expandableelement 30. To achieve this, catheter body 16 may be navigated throughthe vascular system to the desired vascular tissue such as a vessel 66.Examples of vessel 66 may include a left pulmonary vein, a rightpulmonary vein, ostia, or other blood vessel. During deployment of thecatheter 12, expandable element 30 may be deflated for ease of steeringand passage through the vascular system.

Once catheter 12 is adjacent the desired site in vessel 66, expandableelement 30 may be inflated. Generally, inflation of expandable element30 will result in radial expansion of expandable element 30 to adiameter that is at least as large as that of vessel 66. The expandedexpandable element 30 may then be advanced to the opening of vessel 66to achieve contact between expandable element 30 and the opening to theinterior of vessel 66. When the expandable element 30 is properlysituated, the blood flow within the vessel 66 will be occluded.

The occlusion is predicated upon proper positioning of the expandableelement 30 to abut with the opening of vessel 66. As previouslydiscussed, proper positioning presents several challenges to the user.These challenges include the difficulty of navigating catheter 12 withinthe vascular system and the size and nature of the vascular system.Embodiments of the present disclosure utilize one or more temperaturesensors, such as first temperature sensor 62 and second temperaturesensor 64, to ascertain the extent of occlusion (and consequently properlocation) of the expandable element 30.

In use, first temperature sensor 62 is in fluid communication withvessel 66 and measures the temperature of the blood 62 a within vessel66. When there is complete occlusion, blood 62 a becomes stagnant.Second temperature sensor 64 is in fluid communication with vessel 66and measures the temperature of the blood 64 a flowing within vessel 66.Even when there is complete occlusion, blood 64 a keeps flowing.

The first temperature sensor 62 operably measures the temperature ofblood 62 a within a body region 62 b that is in fluid communication withvessel 66. The second temperature sensor 64 operably measures thetemperature of blood 64 a within a body region 64 b that is in fluidcommunication with vessel 66. In an embodiment, the region 62 b is anatrial chamber adjacent the vessel 66. In another embodiment, region 62b may simply be a location that is more distal within vessel 66.Accordingly, a computation of the differential temperature in region 62b and region 64 b can be computed based on the temperature measurementsof the first temperature sensor 62 and the second temperature sensor 64.

The expandable element 30 is shown positioned within vessel 66 inaccordance with principles of the present disclosure. Catheter 12 isnavigated through the vascular system and with the aid of the measureddifferential temperature measurements, expandable element 30 may bepositioned such that its external circumferential surface is in anuninterrupted contact with the opening to the interior of vessel 66. Thecontinuous circumferential contact between the opening of vessel 66 andexpandable element 30 enables complete occlusion of blood flow 62 awithin vessel 66.

First temperature sensor 62 may be used in conjunction with secondtemperature sensor 64 to obtain the differential temperature acrossexpandable element 30; i.e., the difference between the temperature inthe region that is distal to expandable element 30 (region 62 b) and thetemperature in the region that is proximal to expandable element 30(region 64 b). The first temperature at first temperature sensor 62 andthe second temperature at second temperature sensor 64 may be receivedby receiver 33 and processed by processor 37 and/or signal processingunit 58 of control unit 14.

The temperature differential between the first temperature sensor 62,e.g., the distal thermocouple, and the second temperature sensor 64,e.g., the proximal thermocouple, is measured during inflation, prior toinitiating ablation (freezing). Since inflation is performed with a coolfluid which has a temperature below the body temperature of 37° Celsius,there is an initial difference between the first temperature measured atfirst temperature sensor 62 and the second temperature measured atsecond temperature sensor 64.

A continuous supply of blood 64 a at a temperature of 37° Celsius washesthe proximal surface of expandable element 30, e.g., the balloon, andsecond temperature sensor 64. As such, the temperature of the inflationfluid increases due to the heat from the blood 64 a transferring to theinflation fluid, and the second temperature measured at secondtemperature sensor 64 increases to approximately 37° Celsius.

At approximately the same time, as long as the vein, e.g., vessel 66, isstill not occluded, a continuous flow of blood 62 a having a temperatureof 37° Celsius washes the distal surface of expandable element 30 andfirst temperature sensor 62. This causes the temperature of the firsttemperature sensor 62 to increase and remain constant at 37° Celsius.

As full occlusion is achieved, there is no more new blood having a 37°Celsius temperature flowing toward region 62 b. The first temperaturemeasured at first temperature sensor 62 will become lower (colder) thanthe second temperature measured at second temperature sensor 64, as theblood 62 a will become stagnant and will cool due to contact with theexpandable element 30, which is being cooled by the inflation fluid,e.g., the refrigerant.

Since the heat capacity of the inflation fluid inside expandable element30 is low and the inflation volume is also low (approximately 20 cc ofrefrigerant), the temperature difference between the first temperaturemeasured at first temperature sensor 62 and the second temperaturemeasured at second temperature sensor 64 is initially relatively small.Also, the longer it takes a physician to get occlusion, the smaller thedifference between the first temperature measured at first temperaturesensor 62 and the second temperature measured at second temperaturesensor 64 will become. Therefore, it is difficult to ascertain whetherfull occlusion has been achieved, as the first temperature measured atfirst temperature sensor 62 and the second temperature measured atsecond temperature sensor 64 are almost identical.

In addition, this difference in temperature lasts a short period oftime, especially when a bolus injection of refrigerant is used (as noadditional refrigerant is being released into expandable element 30).The initial refrigerant may reach a temperature of 37° Celsius fairlyquickly, making the difference between the first temperature measured atthe first temperature sensor 62 and the second temperature measured atthe second temperature sensor 64 very small. The small difference intemperatures makes it difficult to ascertain whether full occlusion hasbeen achieved, as the effect of cooling is lost in fractions of a secondwhen using a bolus injection of refrigerant.

Therefore, the use a continuous flow of inflation fluid is proposed. Byusing a continuous flow of inflation fluid, the temperature differentialbetween the first temperature measured at the first temperature sensor62 and the second temperature measured at the second temperature sensor64 is maintained. Maintaining the temperature differential may makeocclusion assessment easier. Specifically, when there is completeocclusion, the first temperature at first temperature sensor 62 will bea couple of degrees Celsius lower than the second temperature at secondtemperature sensor 64. The blood 62 a becomes stagnant and becomescolder as it is in contact with the continuous flow of inflation fluid.No more warm blood flows on region 62 b, i.e., blood 62 a is stagnant,which causes the first temperature of first temperature sensor 62 todrop. On the other hand, the second temperature at second temperaturesensor 64 is higher than the first temperature at first temperaturesensor 62, as second temperature sensor 64 is in contact with flowingblood 64 a having a temperature of 37° Celsius. This difference intemperature between the first temperature and the second temperatureindicate full occlusion.

Control unit 14 may be configured to provide a continuous flow ofinflation fluid from fluid supply 52 to the expandable element 30. Theinflation fluid may be precooled prior to injection to a temperature ina range of approximately five degrees Celsius to ten degrees Celsius.Processor 37 may control the flow and amount of the continuous inflationfluid delivered to catheter 12. Processor 37 may be configured toprovide a continuous flow of inflation fluid until a temperaturedifferential that makes the determination of occlusion possible isachieved.

When the continuous flow of inflation fluid is delivered to inflate theexpandable element, the continuous flow of inflation fluid may beinjected at approximately 1,000 to 3,000 standard cubic centimeters perminute. Once it is determined that the extent of occlusion in the bloodvessel 66 is one of a complete occlusion, processor 37 may generate asignal to increase the continuous flow of inflation fluid from fluidsupply 52, so that ablation may be performed. For example, when thecontinuous flow of inflation is delivered to ablate at least a part ofthe blood vessel 66, the continuous flow of inflation fluid is injectedat approximately 6,200 to 7,200 standard cubic centimeters per minute.Two proportional valves with PIDs may be driving the system 10 to havethe continuous flow capability. For example, a high pressureproportional valve and a low pressure proportional valve may be used. APID controller may regulate the injection pressure, regulating the flowand the tip temperature. Of note, although exemplary values have beenprovided for the amount of inflation fluid injected in standard cubiccentimeters per minute, the invention is not limited to such. Theinflation fluid may be injected at any value of standard cubiccentimeters per minute, for example, the injection fluid may be injectedat 9,000 standard cubic centimeters per minute. The volume or mass flowrate may vary depending on different factors, such as the catheter beingused, the treatment to be applied, etc.

The control unit 14 may determine an extent of occlusion in a bloodvessel when the expandable element 30 is inserted within the bloodvessel 66 and inflated, the determining being based at least in part ona relationship of the first temperature measured at first temperaturesensor 62 and the second temperature measured at second temperaturesensor 64. A rate or volume of fluid flowing through the medical device12 may further be controlled using control unit 14. For example, thevolume of fluid sent to expandable element 30 may be sufficientlydimensioned or sized to completely inflate expandable element 30.

For example, using in-vivo or in-vitro modeling, appropriate temperatureprofiles as measured by the first temperature sensor 62 and the secondtemperature sensor 64 can be obtained for the case of occlusion, partialocclusion or no occlusion. These profiles can be incorporated into thecontrol unit 14 and compared with real-time measurements to determineocclusion. Processor 37 may determine whether the extent of occlusion inthe blood vessel 66 is one of complete occlusion, partial occlusion andno occlusion.

In an exemplary embodiment, a large temperature difference, e.g.,greater than two degrees Celsius, between the first temperature measuredby the first temperature sensor 62, and the second temperature measuredby the second temperature sensor 64, may be associated with completeocclusion whereas a temperature difference less than one degree Celsiusmay be associated with no occlusion. Temperature differences of aboveone degree Celsius and below two degree Celsius may be designated ascorresponding to partial occlusion. However, one skilled in the art willappreciate that the temperature variances noted above are merelyillustrative.

In another exemplary embodiment, processor 37 and/or signal processingunit 58 derive an indication of the differential temperature of theblood 62 a in region 62 b and blood 64 a in region 64 b, i.e., the firsttemperature at the first temperature sensor 62 and the secondtemperature at the second temperature sensor 64. To determine thetemperature differential, processor 37 may subtract the secondtemperature from the first temperature. The result is the temperaturedifferential. The temperature differential may be compared against apredetermined value, predetermined values or ranges of values. Processor37 may compare the determined temperature difference to a predeterminedvalue of a plurality of predetermined values, wherein each predeterminedvalue indicates an extent of occlusion in the blood vessel. The extentof occlusion may be determined based at least in part on the comparison.

Similar to the previous example, a predetermined occlusion value may betwo degrees Celsius, e.g., when the temperature differential is equal toor more than two degrees Celsius, then processor 37 determines thatthere is full occlusion. Predetermined partial occlusion values may bevalues that are less than two degrees Celsius but more than or equal toone degree Celsius. When the temperature differential is less than onedegree Celsius, processor 37 may determine that there is no occlusion.

The signal processor in control unit 14 may correlate the differentialtemperature computation with a predetermined value. When completemechanical occlusion has been achieved, the first temperature signalmeasured at first temperature sensor 62 may be continuously measured andcompared against the second temperature signal measured at secondtemperature 64. The predetermined value may be obtained by subtractingthe first temperature signal from region 62 b from the secondtemperature signal from region 64 b. Computations of the differentialtemperature measured at region 62 b and region 62 b may be continuouslyperformed and compared against the predetermined value.

The results of differential temperature computation may be delivered toa user via display 60. Additionally or alternatively, the raw waveformsignals sensed by first temperature sensor 62 and second temperaturesensor 64 may be received control unit 14 and displayed in raw signalwaveform on display 60.

In an embodiment, control unit 14 may provide an indication to a user,such as a clinician of whether or not occlusion has been achieved or ifchanges have arisen based on the sensed signals. For example, controlunit 14 may include a tactile alarm that may be worn by the physician toprovide a vibratory signal to the physician when the signals indicatechanges in the level of occlusion. Control unit 14 may also activate anaudible alarm in response to occlusion changes to alert the clinician toindications of possible changes that may require readjustment of theposition of catheter 12 or even termination of the process. In otherembodiments, light indicators can be used to instruct the physicianabout the level of occlusion: for example, a green light indicatingcomplete occlusion, an orange light indicating partial occlusion and ared light indicating no occlusion.

FIG. 4 illustrates catheter 12 as it would be used within the vascularsystem of a patient. The catheter 12 has the expandable element 30radially expanded by inflation. As further shown in the embodiment, thecatheter 12 is inserted through the vascular system to vessel 66. Thisconfiguration allows use of the catheter 12 by insertion through regions62 b and 64 b, such as a cardiac chamber to abut vessel 66 exiting thechamber. The expandable element 30 is shown positioned near a desiredsite at vessel 66. In this orientation, however, expandable element 30will not completely occlude or block the flow of blood from region 62 bthrough vessel 66 because of the interruptions in the circumferentialcontact with the opening to the interior of vessel 66 at the targetsite. The expandable element 30 is not in contact with region 68,allowing blood 62 a to flow towards region 64 b.

When a complete occlusion is not achieved, both first temperature sensor62 and second temperature sensor 64 are approximately the sametemperature, as the blood flows through both of them. In an alternativeembodiment, first temperature sensor 62 and second temperature sensor 64may serve a dual function, i.e., as a sensor and an electrode. As such,first temperature sensor 62 and second temperature sensor 64 may be usedfor electrical mapping or may be used to provide information about tiplocation during navigation.

The determined temperature difference of the first temperature (measuredat first temperature sensor 62) and the second temperature (measured atsecond temperature 64) may be correlated to a value that indicateswhether there is a complete occlusion of vessel 66. The firsttemperature and the second temperature will have identical orsubstantially identical waveforms for a non-occluded vessel 66. Incontrast, the first temperature and the second temperature will differwhen the vessel 66 is occluded.

If the desired vessel 66 is occluded, the cold stagnant blood 62 a,which has a known temperature—typically, about thirty-seven degreesCelsius—will create a decrease in the temperature measured by the firsttemperature sensor 62 and the temperature measured at first temperaturesensor 62 will indicate that vessel 66 has not been occluded. As such,if there is no blood flow and the blood 62 a is stationary (as in thecase of an occluded vessel), there will be a constant temperaturedifference between the proximal second temperature sensor 64 and thedistal first temperature sensor 62. The temperature of the distal firsttemperature sensor 62 will correspond generally to the temperature ofthe stationary blood, and the temperature of the proximal secondtemperature sensor 64 will correspond generally to the temperature ofthe flowing blood 64 a.

On the other hand, if the vessel is not occluded, the first temperaturesensor 62 and the second temperature sensor 64 will be in contact withthe blood flowing past the expandable element 30, resulting in no orinsignificant change in the temperature difference between the firsttemperature measured at the first temperature sensor 62 and the secondtemperature measured at the second temperature sensor 64. If blood flowis present across the two temperature sensors (as in the case of apartially or non-occluded vessel), the refrigerant will draw heat awayfrom the blood and the temperature difference between the firsttemperature sensor 62 and second temperature sensor 64 will be small orthe same. Several configurations and methods provide the ability tomodify fluid delivery to achieve a constant flow. Accordingly, selectivecontrol of these configurations allows fluid flow to be regulated asdesired.

In an exemplary embodiment, the refrigerant fluid may be pre-cooledbefore inflation. For instance, system 10 may be more efficient if theamount of the N2O refrigerant is pre-cooled by a sub-cooler at controlunit 14. The pressure, density, velocity and the inherentcharacteristics of the fluid may be further modified in order to achievea continuous fluid injection that will maintain a temperaturedifferential and make occlusion assessment easier. Blood or other bodyfluids passing through the vicinity of the thermal device can reduce thequality of thermal exchange with the targeted tissue, which can thennecessitate additional “cooling power” or refrigerant flow in the caseof cryogenic treatments in order to complete the desired treatment.

In an alternative embodiment, the signal of the pressure measurement inregion 62 b and region 64 b may be processed by processor 37 to providea visual representation of a composite waveform that aggregates thesignal waveforms of both region 62 b and 64 b. Alternatively, processor37 may perform signal processing of the sensed signals to provide otherparameters, including but not limited to text, numerical or graphicalrepresentations of the differential temperature.

It should be noted that although the first temperature sensor 62 and thesecond temperature sensor 64 have been disclosed, other forms of sensorsmay alternatively be used to measure other physiologic and hemodynamicparameters in either or both of region 62 b and region 64 b. Forexample, other sensors such as a pressure sensor, flow sensor, an opticsensor, a force sensor, or an electrical sensor or any other suitablesensor known in the art may be substituted.

It will be appreciated by persons skilled in the art that the presentinvention is not limited to what has been particularly shown anddescribed herein above. In addition, unless mention was made above tothe contrary, it should be noted that all of the accompanying drawingsare not to scale. A variety of modifications and variations are possiblein light of the above teachings without departing from the scope andspirit of the invention, which is limited only by the following claims.

What is claimed is:
 1. A method of assessing vein occlusion with anablation catheter, the ablation catheter including: an elongate shaftwith a proximal end, a distal end and a lumen disposed between theproximal end and the distal end; and an expandable element in fluidcommunication with the lumen; the method comprising: measuring a firsttemperature using a first temperature sensor; and measuring a secondtemperature using a second temperature sensor, the first temperaturesensor and the second temperature sensor being longitudinally separatedfrom each other by at least a portion of the expandable element.
 2. Themethod of claim 1, further comprising: delivering a continuous flow ofinflation fluid to the expandable element; and determining an extent ofocclusion in the vein when the expandable element is inserted within thevein and inflated, the determining being based at least in part on arelationship of the first temperature and the second temperature.
 3. Themethod of claim 2, further comprising: determining a temperaturedifference between the first temperature and the second temperature, thetemperature difference indicating the extent of occlusion in the vein.4. The method of claim 2, further comprising: analyzing a firsttemperature signal from the first temperature sensor; analyzing a secondtemperature signal from the second temperature sensor; and deriving atemperature differential between the first temperature sensor and thesecond temperature sensor based at least in part on the analysis of thefirst temperature signal and the second temperature signal.
 5. Themethod of claim 2, wherein the extent of occlusion in the vein is one ofcomplete occlusion, partial occlusion and no occlusion, the methodfurther comprising: increasing the continuous flow of inflation fluidwhen it is determined that the extent of occlusion is one of completeocclusion.
 6. The method of claim 3, further comprising: comparing thedetermined temperature difference to a predetermined value of aplurality of predetermined values, wherein each predetermined valueindicates the extent of occlusion in the vein, and wherein the extent ofocclusion is one of complete occlusion, partial occlusion and noocclusion; and determining the extent of occlusion in the vein based atleast in part on the comparison.
 7. The method of claim 2, wherein whenthe continuous flow of inflation fluid is delivered to inflate theexpandable element, the continuous flow of inflation fluid is injectedat approximately 1,000 to 3,000 standard cubic centimeters per minute.8. The method of claim 7, wherein the inflation fluid is precooled priorto injection to a temperature in a range of approximately five degreesCelsius to ten degrees Celsius.
 9. The method of claim 2, wherein thefirst temperature sensor is positioned distal to the expandable element,and the second temperature sensor is positioned proximal to theexpandable element.
 10. A method of occluding a blood vessel with anablation catheter, the ablation catheter including: an elongate shaftwith a proximal end, a distal end and a lumen disposed between theproximal end and the distal end; and an expandable element in fluidcommunication with the lumen; the method comprising: delivering acontinuous flow of refrigerant to the expandable element at a first flowrate to inflate the expandable element; positioning the expandableelement proximate an ostium of the blood vessel; measuring a firsttemperature using a first temperature sensor; measuring a secondtemperature using a second temperature sensor, the first temperaturesensor and the second temperature sensor being longitudinally separatedfrom each other by at least a portion of the expandable element;determining a difference between the first temperature and the secondtemperature; determining a state of occlusion of the blood vessel basedon the difference between the first temperature and the secondtemperature, the state of occlusion being one of complete occlusion,partial occlusion, and no occlusion; and delivering a continuous flow ofrefrigerant to the expandable element at a second flow rate when thestate of occlusion is determined to be complete occlusion.
 11. Themethod of claim 10, wherein the second flow rate is greater than thefirst flow rate.
 12. The method of claim 11, wherein the first flow rateis between approximately 1,000 standard cubic centimeters per minute andapproximately 3,000 standard cubic centimeters per minute.
 13. Themethod of claim 11, wherein the second flow rate is betweenapproximately 6,200 standard cubic centimeters per minute andapproximately 7,200 standard cubic centimeters per minute.
 14. Themethod of claim 10, wherein the first temperature sensor is positioneddistal to the expandable element and the second temperature sensor ispositioned proximal to the expandable element.
 15. The method of claim10, further comprising: comparing the difference between the firsttemperature and the second temperature to each of a plurality ofpredetermined temperatures, each of the plurality of values being forone of complete occlusion, partial occlusion, and no occlusion; anddetermining the extent of occlusion based on the comparison between thedifference between the first temperature and the second temperature andeach of the plurality of predetermined temperatures.
 16. The method ofclaim 10, wherein the refrigerant delivered to inflate the expandableelement is precooled prior to delivery to the expandable element. 17.The method of claim 16, wherein the refrigerant is precooled to atemperature within a range of approximately five degrees Celsius toapproximately 10 degrees Celsius.
 18. A method of assessing blood vesselocclusion by an expandable element of a medical device, the methodcomprising: precooling refrigerant to a temperature betweenapproximately 5° C. and approximately 10° C.; delivering a continuousflow of the refrigerant to the expandable element at a first flow rateof between approximately 1,000 to 3,000 standard cubic centimeters perminute to inflate the expandable element; measuring with a firsttemperature sensor a first temperature within the blood vessel, thefirst temperature sensor being located distal to the expandable element;measuring with a second temperature sensor a second temperature within abody region that is in fluid communication with the blood vessel, thesecond temperature sensor being located proximal to the expandableelement; determining a difference between the first temperature and thesecond temperature; determining a state of occlusion of the blood vesselby the expandable element based on the difference between the firsttemperature and the second temperature, the state of occlusion being oneof complete occlusion, partial occlusion, and no occlusion; anddelivering a continuous flow of the refrigerant to the expandableelement at a first flow rate of between approximately 6,200 to 7,200standard cubic centimeters per minute when the state of occlusion isdetermined to be complete occlusion.
 19. The method of claim 18, furthercomprising controlling the delivery of the continuous flow of therefrigerant at the first flow rate and the second flow rate with atleast one proportional valve with a PID controller.
 20. The method ofclaim 18, wherein the blood vessel is a pulmonary vein.